Geothermal Resource¶
In pythermogis we consider reservoirs with natural permeability. These can be sedimentary rocks and (fractured) basement/magmatic geothermal reservoirs.
- Sedimentary rocks: These are typically characterized by their stratigraphy, lithology, and for clastic rocks are often marked by primary (matrix pore space related) porosity and permeability, whereas carbonate rocks are often characterized by secondary porosity and permeability due to dissolution and fracturing.
- Fractured basement/magmatic rocks: Flow characteristics are often related by their fracture networks, which can significantly influence fluid flow.
Geothermal Resource Parameters¶
The geothermal resource parameters based on (upscaling) of resource parameters based on resource type and should include:
- Aquifer top depth ztop^: The depth at which the geothermal resource is located, typically measured in meters below ground level.
- Aquifer thickness H: The vertical extent of the geothermal resource, which can influence the amount of heat available.
- Temperature Taq: The temperature of the geothermal resource, which is a critical factor in determining its energy potential.
- Reservoir flow properties k and por: These include permeability and porosity
- Salinity s: The concentration of dissolved salts in the geothermal fluid, which influence temperature (and pressure) dependent properties such as density and viscosity.
These can be specified as site-specific parameters, or as a grid input, and a number of them as a distribution of values to account for uncertainties in the reservoir properties.
| Technical parameter | symbol | value | unit |
|---|---|---|---|
| Aquifer/fracture zone top depth | ztop | varies | m |
| Aquifer/fracture zone thickness | H | 10-500 | m |
| aquifer net-to-gross | Ng | 1 | - |
| aquifer porosity | por | 0.05-0.4 | - |
| aquifer permeability | k | fixed or f(porosity) | millidarcy |
| aquifer temperature | Taq | temperature model at z+0.5H | °C |
| aquifer water salinity | s | Equation | ppm |
| aquifer water salinity at z=0 | s0 | 0 | ppm |
| aquifer water salinity gradient | sgrad | 45-70 | ppm/m |
| aquifer kh/kv ratio | Kh_kv | 1-10 | - |
| return temperature | Tinj | Application dependent | °C |
The depth dependent salinity s (ppm) is based on the following equation:
s=s₀+ sgrad (ztop+0.5H)
where z is top depth and H thickness of the aquifer, both in m
- s₀ is the salinity at the top of the aquifer (z=0), typically 0 ppm for freshwater aquifers.
- sgrad is the salinity gradient, which is the increase in salinity with depth, typically around 47 ppm/m for freshwater aquifers.
- The salinity gradient is typically around 45-70 ppm/m for sedimentary aquifers, which means that the salinity increases by 47-70 ppm for every meter of depth measured from surface
In the Netherlands aquifers with salinities up to 180,000 ppm do not give any problems in production.